Preparation of highly hydrated self-supporting hyaluronic acid containing films

ABSTRACT

This invention provides new gels in the form of highly hydrated self-supporting film, comprising one or more alkaline alginates, an alkaline earth alginate, a polyalcohol and a hyaluronic acid or a derivative thereof, and their preparation process. These polysaccharide-matrix gels in highly hydrated self-supporting film form are suitable for use as covering and protection materials for cutaneous lesions and/or pathologies in that they are obtainable in self-supporting form in the desired thickness, are transparent, flexible, have good mechanical characteristics, are adaptable to the lesion surface without strongly adhering to it, and are permeable to gas but are impermeable to liquids and bacteria; one or more pharmacologically active substances can also be incorporated in the gel.

This application is a divisional of application Ser. No. 07/707,790, filed on May 30, 1991, now U.S. Pat. No. 5,523,093 the entire contents of which are hereby incorporated by reference.

FIELD OF THE INVENTION

This invention relates to new gels in the form of highly hydrated self-supporting films, the process for their preparation and their use in the therapy of cutaneous lesions and/or pathologies.

PRIOR ART

Hydrogels consisting of synthetic or semisynthetic polymers or synthetic polymers with small additions of natural polymers and having the characteristic of being only slightly or not reabsorbable are already known for the treatment of cutaneous lesions.

Xerogels, i.e., anhydrous gels consisting of fibres of calcium alginate presented in the form of bioreabsorbable unwoven tissue, are also known.

Protective films of various types used for treating cutaneous lesions are also known.

For example, DE patent 30 17 221 describes an ointment containing a soluble alkaline metal alginate salt which when applied to the lesion and treated in situ with a soluble calcium salt forms a protective film of Ca alginate. To obtain this film the ointment must be reconstituted at the moment of use.

WO patent 80/02300 describes the process for preparing an unwoven tissue based on calcium alginate fibres.

U.S. Pat. No. 4,393,048 describes a gel containing an alkaline metal alginate and glycerol for wound medication which on drying forms a protective adhering film, and U.S. Pat. No. 4,391,799 describes the same gel in association with silver salts for treating white phosphorus burns.

European patent application EPA 83301149.7 describes wound medications in the form of hydrogel membranes composed of hydrophilic biopolymers derived from keratin, glycosaminoglycan or collagen.

U.S. Pat. No. 4,664,105 describes a wound medication composed of granulated cellulose material or a polysaccharide.

Gels in the form of highly hydrated self-supporting alginate-based film have never been described.

An object of the present invention is to provide a wound medication in the form of a thin self-supporting film which maintains a high degree of hydration for a prolonged time, this being of known and considerable importance for the repair to take place in a short time and within the dictates of the process physiology, to result in cicatrices with optimum characteristics both from the physiological and from the aesthetic aspect.

A further object of the present invention is to provide a wound medication in the form of a bioreabsorbable film, this characteristic allowing the medication to be replaced at a much lesser rate, thus avoiding further irritation to the lesion and facilitating the reparative process.

A further object of the invention is to provide a wound medication in the form of a film with good mechanical characteristics which is soft, pliable, easily handled and properly adaptable to the lesion, but which is only slightly adhesive and can therefore be easily removed without damaging the newly formed tissues, and further which is non-toxic, sterilizable in an autoclave and by gamma rays, compatible with a large number of drugs, therefore allowing their incorporation, does not need to be reconstituted at the moment of use, can absorb exudates, is permeable to gases but not to liquids or bacteria, and which is transparent to enable the development of the reparative process to be followed.

A further object of the invention is to provide a medication which is economically valid in that it reduces the number of medications required.

SUMMARY OF THE INVENTION

These and further objects are attained by the composition according to the present invention, which relates to new gels characterised by being in the form of highly hydrated self-supporting film comprising one or more alkaline alginates, an alkaline earth alginate, a polyalcohol and a natural, synthetic or semisynthetic polymer of hydrophilic character. In one embodiment of the invention a medicament is dispersed within the gel. These gels in highly hydrated self-supporting film form are prepared by a new process which together with the use of the new film in the therapy of human lesions and/or pathologies also form part of the invention.

DETAILED DESCRIPTION

The gel in highly hydrated self-supporting film form according to the present invention contains a quantity of between 1% and 7.5%, and preferably 3.5%, (all percentages being by weight) of one or more alkaline alginates, preferably sodium alginate; a quantity of between 0.1% and 5%, and preferably 1%, of an alkaline earth alginate, preferably calcium alginate; a quantity of between 0.1% and 10%, and preferably 5%, of a polyalcohol, preferably glycerol; and a quantity of between 0.05% and 10%, and preferably 0.5%, of a natural, synthetic or semisynthetic polymer of hydrophilic character, preferably sodium hyaluronate, plus optionally between about 0.01% and 10% of one or more medicaments, the remainder being water. Other alkaline alginates which can be advantageously used are for example potassium and ammonium alginates.

The described film is obtained with the required characteristics according to the invention by starting from an initial fluid gel containing a quantity of between 3.5% and 7.5%, and preferably 3.5%, of one or more alkaline alginates, preferably sodium alginate, a quantity of between 0.5% and 7.5%, and preferably 5%, of a polyalcohol, preferably glycerol, a quantity of between 0.1% and 10%, and preferably 0.2%, of a natural, synthetic or semisynthetic polymer of hydrophilic character, preferably sodium hyaluronate, plus optionally a medicament.

The initial fluid gel is extruded by pumping through a slit of adjustable width and thickness, and coagulated by passage through between 2 and 4 successive baths, preferably 2, at controlled temperature, the baths containing one or more soluble calcium salts.

The concentration of Ca²⁺ ions in the various coagulation baths is between 0.1 and 10% and preferably 1% in the first coagulation bath, and 2% in the subsequent baths.

The coagulation bath temperature is between 15° C. and 40° C. and preferably 20° C. for the first, and 30° C. for the subsequent baths. After passage through the last coagulation bath a highly hydrated gel is obtained in the form of a self-supporting thin film having a thickness variable between 0.1 and 5 mm, preferably 0.4 mm, with a pH of between 5.5 and 7.5, preferably between 6.5 and 7.2. The final film characteristics, such as its mechanical and hydration characteristics, can be varied according to requirements by varying the initial gel composition and the coagulation bath conditions.

In a preferred embodiment of the process according to the invention, the alginate film is prepared by extrusion and coagulation using the device shown in FIG. 1.

The initial fluid gel is placed in a container vessel 1 from which it is drawn by a pump 2 operating at a suitable r.p.m., then passed through a filter 3 and fed to the filming extruder 4 comprising a slit of suitable variable size immersed in the first coagulation bath.

Coagulation occurs immediately on leaving the filming extruder, the recovered film being passed below a guide drum 5 immersed in the first coagulation bath. The film then leaves the bath, passes through a dragging roller 6 driven by a motor 7, enters a second coagulation bath through which it is guided by a second drum 8, leaves the bath guided by a third drum 9 and is wound onto a winding reel 12 by a calender 10 driven by a motor 11.

The size-setting of the extruder, the pump r.p.m., the dragging roller speed and the winding roller speed can be varied to define the final characteristics of the film.

For example a film according to the present invention with a thickness of 300μ is obtained by using the device of FIG. 1 under the following operating conditions:

pump r.p.m.: 15 r.p.m. equivalent to a throughput of 18 cc/min

size setting of filming extruder: 200μ

dragging roller r.p.m.: 2.15 r.p.m.

temperature 1st bath (CaCl₂ 1% w/v): 20° C.

temperature 2nd bath (CaCl₂ 2% w/v): 27° C.

extruded film length produced per minute: 0.4 m.

Any active principle compatible with the gel composition, such as substances of antiseptic, antibiotic, anti-inflammatory, antihistaminic or other activity, can be incorporated into the gel either alone or in association. The concentration of the active principle incorporated into the gel depends on its pharmacological characteristics, and would represent a quantity such as to make it effective for the purpose of the specific application. The medicament quantity in the compositions of the invention can vary from about 0.01% to 10% of the weight of the final product.

The film obtained in this manner can be easily stored, handled and used advantageously as covering or medication material for cutaneous lesions and/or pathologies such as the treatment of wounds of surgical or traumatic origin, burns or lesions of pathological origin such as stasis ulcers, bedsores and the like.

Some non-limiting examples of the preparation of self-supporting film according to the invention are described below.

EXAMPLE 1

24.5 g of sodium alginate are dispersed at ambient temperature in 250 ml of water under continuous stirring. A viscous gel forms, to which are added 1.4 g of sodium hyaluronate Hyalastine fraction (European patent EP 0138572 granted on 25^(th) July 1990), 35 g of glycerol and 7 g of NaCl dissolved in 250 ml of water under stirring, the final solution volume then being adjusted to 700 ml. Slow stirring, to avoid incorporating air, is then continued for about 20 hours, after which the viscous solution is filtered through a 20μ mesh filter and degassed under vacuum.

The solution is extruded by pumping through a slit of width 12 cm and of set thickness, and is coagulated by passing through two successive baths containing calcium chloride, the first at 20° C. with a concentration of 1% and the next at 30° C. with a concentration of 2%. The film obtained, having a thickness of about 0.250 mm, is wound on a suitable spool, washed by immersion in a water bath for 1 hour and finally stored in an aqueous solution containing 5% glycerol, 0.2% methylparaben, 0.02% propylparaben and 0.2% sodium dehydroacetate.

EXAMPLE 2

Following the procedure described in Example 1, 1.4 g of sodium hyaluronate Hyalectine fraction (European patent EP 0138572 granted on 25^(th) July 1990) are added in place of the Hyalastine fraction, to obtain a film having analogous characteristics to those of the film obtained in Example 1.

EXAMPLE 3

50 ml of an aqueous solution containing 0.4 g of hyaluronic acid ethyl ester of 75% esterification (HYAFF 7 P75 European patent application EPA 216453 of Jul. 7, 1986) are added to 150 ml of an aqueous solution containing 7 g of sodium alginate, 10 g of glycerol and 2 g of NaCl. After filtration and degassing, the final solution is extruded and coagulated by the procedure described in Example 1 to obtain 150 g of film with a thickness of 0.250 mm. The film is stored in the solution of glycerol and preservatives described in Example 1.

EXAMPLE 4

50 ml of an aqueous solution containing 5 g of polyethyleneglycol 1500 are added to 150 ml of an aqueous solution containing 7 g of sodium alginate, 10 g of glycerol and 2 g of NaCl. After filtration and degassing, the final solution is extruded and coagulated by the procedure described in Example 1 to obtain 150 g of film with a thickness of 0.250 mm. The film is stored in the solution of glycerol and preservatives described in Example 1.

EXAMPLE 5

50 ml of an aqueous solution containing 2.5 g of p-(aminomethyl) benzenesulphonamide acetate are added to 150 ml of an aqueous solution containing 7 g of sodium alginate, 10 g of glycerol and 2 g of NaCl. After filtration and degassing, the final solution is extruded and coagulated by the procedure described in Example 1 to obtain 150 g of film with a thickness of 0.250 mm. The film is stored in the solution of glycerol and preservatives described in Example 1.

EXAMPLE 6

50 ml of an aqueous solution containing 0.1 g of the neomycin salt of hyaluronic acid partly esterified with ethanol (75% of the carboxyl groups esterified with ethanol, 25% of the carboxyl groups esterified with neomycin in accordance with Example 29 of European patent application EPA 216453 filed on Jul. 7, 1986) and 0.3 g of the 75% esterified partial ethyl ester of hyaluronic acid are added to 150 ml of an aqueous solution containing 7 g of sodium alginate, 10 g of glycerol and 2 g of NaCl. After filtration and degassing, the final solution is extruded and coagulated by the procedure described in Example 1 to obtain 150 g of film with a thickness of 0.250 mm. The film is stored in the solution of glycerol and preservatives described in Example 1. The final neomycin content of the film is 0.00305 g/100 g.

EXAMPLE 7

50 ml of an aqueous dispersion of 10 g of microbeads obtained from mixed ethyl and hydrocortisone ester of hyaluronic acid (Example 15 of European patent application EPA 216453 of Jul. 7, 1986) are added to 150 ml of an aqueous solution containing 7 g of sodium alginate, 10 g of glycerol and 2 g of NaCl. The final dispersion is extruded and coagulated by the procedure described in Example 1 to obtain 150 g of film with a thickness of 0.250 mm. The film is stored in the solution of glycerol and preservatives described in Example 1.

To demonstrate the advantages and activity of the highly hydrated self-supporting film according to the present invention a trial was conducted using 45 male Sprague-Dawley rats of weight 225-250 g. The rats were divided into three groups and were given a heat lesion by a suitable instrument containing a metal prod of known area able to maintain a constant temperature. By applying this instrument to the back of the animal in a region close to the caudal reproducible heat lesions were obtained classifiable as third degree burns.

The treatment scheme involved a group of untreated animals, a group of animals treated conventionally with vaselin gauze and a third group treated with a film of hydrated gel as described in Example 1 of the present patent. The medications were changed every 3 days, 5 animals of each group being sacrificed 9, 15 and 25 days after the lesion. After a planimetric evaluation of the lesion area and eschar area, biopsies were taken for histological examination. The results of these tests are given in Table 1.

                                      TABLE 1                                      __________________________________________________________________________                 day 9   day 15   day 25                                                        NT GG G NT GG G  NT GG G                                           __________________________________________________________________________     Persistence of eschar                                                                      +  +  + +  +  ±                                                                              +  ±                                                                              -                                           Reduction in lesion area                                                                   -  -  ±                                                                             -  -  +  -  ±                                                                              ++                                          Neoangiogenesis                                                                            -  -  + -  -  ++ -  -  +++                                         __________________________________________________________________________      NT = not treated; GG = vaselin gauze; G = gel film                             - = not apparent; ± = hardly apparent; + = apparent; ++ = very              apparent; +++ = extremely apparent                                       

The results summarized in the table show that burns treated with the composition described in Example 1 of the present patent have a positive effect on early eschar fall, reduction in lesion area and neovascularization. 

We claim:
 1. A process for preparing a hydrated self supporting gel film containing the following components:i) from 1 to 7.5% by weight of one or more alkaline alginates and/or ammonium alginate, ii) from 0.1 to 5% of an earth alkaline alginate, iii) from 0.1 to 10% by weight of a polyhydric alcohol, iv) from 0.05 to 10% by weight of a polymer having a hydrophilic character selected from the group consisting of hyaluronic acid and a derivative thereof, v) the remainder being water said process comprising the following steps: a) preparing an initial fluid gel containing the following components: i') from 3.5 to 7.5% by weight of said alkaline alginates and/or ammonium alginate ii') from 0.5 to 7.5% by weight of said polyhydric alcohol, iii') from 0.1 to 10% by weight of said polymer having hydrophilic character, b) extruding the initial fluid gel obtained in the preceding step by pumping it through a slit of adjustable width and thickness to provide an extruded film, c) coagulating said extruded film by passing it through from 2 to 4 successive coagulation baths, said coagulation baths containing one or more earth alkaline salts, wherein the concentration of the earth alkaline ion in said baths is 1% in the first bath, and 2% in the subsequent baths at temperatures of 20° C. for the first bath and 30° C. for the successive baths.
 2. The process as claimed in claim 1, wherein said earth alkaline alginate is calcium alginate, and wherein step (c) is carried out by using successive coagulation baths containing calcium salts.
 3. The process as claimed in claim 2, wherein said hydrated self supporting gel film contains an alkaline alginate salt selected from the group consisting of: sodium alginate, potassium alginate and mixtures thereof.
 4. The process as claimed in claim 1, wherein said polyhydric alcohol is glycerol.
 5. The process as claimed in claim 1, wherein, when said polymer of hydrophilic character is a hyaluronic acid derivative selected from the group consisting of hyaluronic acid sodium salt, the neomicin salt of hyaluronic acid having 75% of carboxylic acid esterified with ethyl alcohol, the hyaluronic acid partial ester having 75% of carboxylic functions esterified with ethyl alcohol, and the mixed ethyl and hydrocortisone ester of hyaluronic acid, having 80% of carboxylic groups esterified with ethanol and 20% esterified with hydrocortisone.
 6. The process as claimed in claim 1, wherein said hydrated self supporting film contains the following components:i) 3.5% by weight of one or more alkaline alginates and/or ammonium alginate, ii) 1% of an earth alkaline alginate and/or ammonium alginate, iii) 5% by weight of a polyhydric alcohol, iv) 0.5% by weight of a polymer having a hydrophilic character selected from the group consisting of hyaluronic acid and a derivative thereof, vi) the remainder being water; and wherein the initial fluid gel prepared in step (a) contains the following components: i') 3.5% by weight of at least one member selected from the group consisting of said alkaline alginates and ammonium alginate, ii') 5% by weight of said polyhydric alcohol, iii') 0.2% by weight of said polymer having hydrophilic character.
 7. The process according to claim 6, wherein step (c) is carried out in 2 successive baths.
 8. The process according to claim 1, wherein step (b) and (c) are carried out in a device comprising the following items:a container vessel, a pump, a filter, a first coagulation bath, a filming extruder comprising a slit of suitable variable size, immersed in said first coagulation bath, a guide drum immersed in said first coagulation bath, a second coagulation bath, a dragging roller placed between the first and the second coagulation bath, driven by a motor, a second guide drum immersed in the second coagulation bath, placed above the second coagulation bath, a winding reel, and a calendar driven by a motor.
 9. The process according to any one of claims 1-8, wherein said hydrated self-supporting gel film additionally comprises from 0.01 to 10% by weight of an active principle. 